A combined cycle thermal power plant has been used at a thermal power plant to improve thermal efficiency and operative efficacy for cost cutting of generating the electric power. The combined cycle thermal power plant has a gas turbine and a steam turbine as an engine, and drives an electric generator by both the gas turbine and the steam turbine. That is, high efficiency is achieved by burning fuel in a burner to drive the gas turbine, guiding the discharged gas from the gas turbine to an exhaust heat recovery boiler, and driving the steam turbine by the steam generated by the exhaust heat recovery boiler. Normally, the combined cycle thermal power plant is comprised of a plurality of units where each unit includes a gas turbine and a steam turbine, and forms a one-shaft configuration where each unit is connected to one electric generator.
Even for a high efficiency power plant such as a combined cycle thermal power plant, it is important, for the purpose of heat efficiency management, to investigate a cause of decrease in the heat efficiency. In such a case, it is necessary to know whether the decrease in the heat efficiency is caused by the gas turbine, the steam turbine, or other major constituents.
In order to identify the cause of the heat efficiency change in the combined cycle thermal power plant, an optical torque measurement apparatus has been developed that can detect torque of a driving shaft (rotating body) of the engine such as the gas turbine or the steam turbine. The torque measurement apparatus places a pair of reflectors which are spaced apart in the axial direction on the surface of the rotating body. A laser light is applied to the surface of the rotating body where the pair of reflectors is placed and the reflected light therefrom is received. A delay time of the reflected light from the reflector is measured. Based on the delay time of the reflected light from the reflector, the amount of torsion of the rotating body is detected. The torque of the rotating body is measured based on the torsion amount as shown, for example, in FIG. 1 of Japanese Patent Laid-Open Publication No. 2002-22564.
Since the torque measured by the torque measurement apparatus is accurate and the torque of the engine corresponds to the output of the engine, an output of an engine such as a gas turbine output or a steam turbine output can be measured accurately.